Apparatus and method for continuous additive manufacturing

ABSTRACT

An apparatus for continuous powder-based additive manufacturing of a large annular object or multiple smaller objects simultaneously is described. The build unit(s) of the apparatus includes a powder delivery mechanism, a powder recoating mechanism and an irradiation beam directing mechanism. The build unit(s) is attached to a rotating mechanism such that the build unit(s) rotates around and above the annular powder bed during production. The rotating mechanism is supported onto a central tower, and both the rotating mechanism and the tower are concentric with the non-rotating annular powder bed. An additive manufacturing method using the apparatus involves repetitive and continuous cycles of at least simultaneously rotating the build unit(s) to deposit powder onto the powder bed and irradiating the powder to form a fused additive layer. The continuous additive manufacturing process may be further aided with a helical configuration of the powder bed build surface.

INTRODUCTION

The present disclosure generally relates to additive manufacturingapparatuses and methods. More specifically, the present disclosurerelates to apparatuses and methods that enable a continuous process ofadditively manufacturing a large annular object or multiple smallerobjects simultaneously, such as but not limited to components of anaircraft engine.

BACKGROUND

Additive manufacturing (AM) encompasses a variety of technologies forproducing components in an additive, layer-wise fashion. In powder bedfusion which is one of the most popular AM technologies, a focusedenergy beam is used to fuse powder particles together on a layer-wisebasis. The energy beam may be either an electron beam or laser. Laserpowder bed fusion processes are referred to in the industry by manydifferent names, the most common of which being selective lasersintering (SLS) and selective laser melting (SLM), depending on thenature of the powder fusion process. When the powder to be fused ismetal, the terms direct metal laser sintering (DMLS) and direct metallaser melting (DMLM) are commonly used.

A description of a typical laser powder bed fusion process is providedas follows. Referring to FIG. 1, a laser powder bed fusion system suchas the system 100 includes a fixed and enclosed build chamber 150.Inside the build chamber 150 is a build plate 106 that is flanked by afeed powder reservoir 104 at one end and an excess powder receptacle 130at the other end. During production, an elevator 102 in the feed powderreservoir 104 lifts a prescribed dose of powder above the level of abuild plate 106. The prescribed dose of powder is then spread in a thin,even layer 132 over the build surface 108 by a recoater mechanism 110.For example, as shown in FIG. 1, the powder is spread in a direction asindicated by the arrow 112. Overflows from the build plate 106 arecollected by the excess powder receptacle 130, then optionally treatedto sieve out rough particles before re-use. Current powder bedtechnologies are discrete and intermittent in that the laser or electronbeam must pause to wait for the subsequent layer of powder to beleveled.

The recoater mechanism 110 may be a hard scraper, a soft squeegee, or aroller. A selective portion of the powder 114 that corresponds to a“slice” or a layer of the part to be manufactured is then sintered ormelted by a focused laser 116 scanning across the surface of theselective portion 118. In other words, the powder layer 132 is subjectedto laser radiation in a site-selective manner in dependence oncomputer-aided design (CAD) data, which is based on the desired geometryof the work piece that is to be produced. The laser irradiation sintersor melts the raw material powder, and the sintered/melted area thenre-solidifies and re-crystallizes into a fused region of the work piece.

Using a plurality of movable mirrors or scanning lenses, a galvanometerscanner 120 moves or scans the focal point of the unfocused laser beam126 emitted by the laser source 128 across the build surface 108 duringthe SLM and SLS processes. The galvanometer scanner in powder bed fusiontechnologies is typically of a fixed position but the movablemirrors/lenses contained therein allow various properties of the laserbeam to be controlled and adjusted.

As of now, powder bed technologies have demonstrated the best resolutioncapabilities of all known metal additive manufacturing technologies.However, since the build needs to take place in the powder bed,conventional machines use a large amount of powder. For example, apowder can be over 130 kg or 300 lbs. This is costly and wasteful,especially considering the environment of a large facility using a largenumber of machines. The powder that is not directly sintered or meltedinto the built object but is nevertheless distributed over the powderbed is problematic because not only does it add weight to the elevatorsystems (conventional powder beds are typically lowered as successivelayers of powder are built up), complicate seals and chamber pressure,it is detrimental to object retrieval at the end of the built, andbecomes unmanageable in large bed systems that are currently beingconsidered for large objects. For instance, the amount of powder neededto make a large object may exceed the limits of the powder bed or makeit difficult to control the lowering of the powder bed at a precisionthat is sufficient to make highly uniform additive layers in the objectbeing built.

In view of the foregoing, there exists a need for additive manufacturingapparatuses and methods that can handle production of large objects withimproved precision and in a manner that is both time- and cost-efficientwith a minimal waste of raw materials.

SUMMARY

In a first aspect, the present invention relates to an additivemanufacturing apparatus that includes at least one build unit thatcomprises a powder delivery mechanism, a powder recoating mechanism andan irradiation beam directing mechanism; a build platform; and arotating mechanism to which at least a portion of the at least one buildunit is attached that provides rotational movement around a center ofrotation to the at least one build unit, such that the at least onebuild unit moves in a circular path about the center of rotation.Preferably, the build platform is annular. Preferably, the buildplatform and the rotating mechanism are concentric.

In certain embodiments, the apparatus further includes a tower ontowhich the rotating mechanism is supported. the build platform, therotating mechanism and the tower are concentric.

Preferably, the build platform and the rotating mechanism areconcentric.

Preferably, at least portion of the at least one build unit is attachedto the circumference of the rotating mechanism.

In certain embodiments, the apparatus further includes a build chamberencasing the apparatus.

In certain embodiments, the apparatus further includes a support arm,wherein at least portion of the at least one build unit is attached tothe rotating mechanism via the support arm.

In some embodiments, the build platform includes an inner wall and anouter wall. In one embodiment, the inner wall and the outer wall eachinclude one or more receptacles to catch powder spillover.

In one embodiment, the build platform is non-rotating and verticallystationary. In an alternative embodiment, the build platform isnon-rotating and vertically movable.

In some embodiments, the tower is vertically movable.

In some embodiments, the irradiation beam directing mechanism includes alaser source or an electron source.

In some embodiments, the build platform includes a build surface thathas a helical configuration.

In a second aspect, the present invention relates to a method ofmanufacturing at least one object. The method includes the steps of: (a)rotating at least one build unit around a center of rotation to depositpowder onto a build platform, such that the at least one build unitmoves in a circular path about the center of rotation; (b) irradiatingat least one selected portion of the powder to form at least one fusedlayer; and (c) repeating at least steps (a) and (b) to form the at leastone object. In some embodiments, the method further includes a step (d)of leveling the at least one selected portion of the powder. Preferably,at least steps (a), (b) and (d) are carried out simultaneously andcontinuously. In some embodiments, the method further includes a step ofmoving the build platform vertically.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an exemplary prior art powder-based system for additivemanufacturing.

FIG. 2A is a schematic front cross-sectional view of a large-scaleadditive manufacturing apparatus according an embodiment of the presentinvention with an annular powder bed and a mechanism that rotates thebuild unit.

FIG. 2B is a B-B′ side cross-sectional view of the large-scale additivemanufacturing apparatus of FIG. 2A.

FIG. 2C is a schematic top view of the large-scale additivemanufacturing apparatus of FIG. 2A.

FIG. 3 is a schematic top view of a large-scale additive manufacturingapparatus according an embodiment of the present invention with anannular powder bed and a mechanism that rotates multiple build units.

FIG. 4A is a perspective view of a single-helical floor of an annularpowder bed according an embodiment of the present invention.

FIG. 4B is a perspective view of a triple-helical floor of an annularpowder bed according an embodiment of the present invention.

FIG. 5A is a top view of a large-scale additive manufacturing apparatusaccording to an embodiment of the present invention, where the annularpowder bed has a triple helical floor.

FIG. 5B is a C-C′ side cross-sectional view of the large-scale additivemanufacturing apparatus of FIG. 5A.

FIG. 6A is a schematic top view of a large-scale additive manufacturingapparatus with a large stationary powder delivery mechanism.

FIG. 6B is an D-D′ side cross-sectional view of the large-scale additivemanufacturing apparatus of FIG. 6A.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appendeddrawings is intended as a description of various configurations and isnot intended to represent the only configurations in which the conceptsdescribed herein may be practiced. The detailed description includesspecific details for the purpose of providing a thorough understandingof various concepts. However, it will be apparent to those skilled inthe art that these concepts may be practiced without these specificdetails. For example, the present invention provides a preferred methodfor additively manufacturing metallic components or objects, andpreferably these components or objects are used in the manufacture ofjet aircraft engines. In particular, large, annular components of jetaircraft engines can be advantageously produced in accordance with thisinvention. However, other components of an aircraft and othernon-aircraft components may be prepared using the apparatuses andmethods described herein.

The present invention provides a large-scale additive manufacturingapparatus and embodiments of the apparatus that can be used to performpowder bed based additive manufacturing, including but not limited toselective laser sintering (SLS), selective laser melting (SLM), directmetal laser sintering (DMLS), direct metal laser melting (DMLM) andelectron beam melting (EBM) processes. The present invention alsoincludes methods for utilizing the apparatus or an embodiment thereof toadditively manufacture objects. The apparatus of the present inventionincludes components that make it particularly useful for making largeobjects that are substantially annular or cylindrical in a continuousmanner where the powder deposition, powder leveling, beam irradiationand vertical sliding of the central tower and/or powder bed can occursimultaneously. As used herein, the term “continuous” means that aprocess or a specific step of a process or a movement (e.g. powderdeposition, powder leveling, beam irradiation or vertical sliding of thecentral tower and/or powder bed) is uninterrupted in time and has nointerstices or intervals of time. As used herein, the term“simultaneous” means that two or more processes or specific steps of aprocess (powder deposition, powder leveling, beam irradiation andvertical sliding of the central tower and/or powder bed) are takingplace concurrently or coincidentally in time. Examples of thesesubstantially annular or cylindrical objects are annular or cylindricalcomponents of an aircraft engine or an aircraft. Examples of suchaircraft components are turbine or vane shroudings, central engineshaft, casings, compressor liners, combustor liners, ducts, etc. In someinstances, these components can have a radius of up to 2 meter.Additionally, multiple smaller objects can be arranged appropriately onthe build platform to be simultaneously built.

Accordingly, an additive manufacturing apparatus of the presentinvention includes an annular powder bed instead of a conventionalrectangular powder bed. There is provided a rotating mechanism, to whicha build unit is attached. The build unit includes a powder deliverymechanism, a powder recoating mechanism and an irradiation beamdirecting mechanism. The rotating mechanism, which is preferablyconcentric with the powder bed, positions the build unit above andsuitably substantially parallel to the annular powder bed androtationally moves the build unit above and suitably substantiallyparallel the powder bed to simultaneously level powder and melt powderto form a fused layer of the build object at one or more build areaswithin the powder bed. In some embodiments, the rotating mechanism isattached and supported onto a central, erect tower which is alsopreferably concentric with the non-rotating annular powder bed.

As used herein, the term “mechanism” refers to a structural entity thatis either single device or instrument, a single device or instrumenthaving multiple components, or a system of multiple, distinct devices orinstruments. The term “mechanism” is used interchangeably with the term“unit”, which bears the same definition as set forth in the foregoingsentence.

FIG. 2A is a schematic front cross-sectional view of a large-scaleadditive manufacturing apparatus 200 in accordance with an embodiment ofthe present invention. The apparatus 200 includes an annular powder bed202 and a build unit 208. The annular powder bed 202 has a buildplatform 228, a circular inner wall 224 and a circular outer wall 222with a diameter that is greater than the diameter of the inner wall 224.At the beginning of a powder-based additive manufacturing process, theraw material powder is deposited onto the build surface 242 which is thetop surface of the build platform 228. In some embodiments, such as theembodiment shown in FIG. 2A, the inner and outer walls 224, 222 of theannular powder bed 202 each include a receptacle 226 to capture unfusedpowder spillover during production. The apparatus 200 further includes abuild unit 208 which has several components each serving differentfunctions in a powder-based additive manufacturing process such as butnot limited to selective laser melting (SLM), direct metal laser melting(DMLM) and electron beam melting (EBM). Among the components of thebuild unit 208 are, for example, a powder delivery mechanism 214 (e.g. ahopper), an irradiation beam directing mechanism 212 and a recoatingmechanism 216. The recoating mechanism 216 may be a scraper, blade,squeegee, roller or the like.

During an additive manufacturing process, the powder delivery mechanism214 directionally delivers and deposits a raw material powder 230 ontoand/or into the powder bed 202. The powder recoating mechanism 216directionally spreads and levels the deposited powder 230 into asubstantially even powder layer, and a portion of this substantiallyeven powder layer (i.e. a build area) is then melted by the laser orelectron beam emitted by the irradiation beam directing mechanism 212 toform a fused, additive layer of the built object 220. This irradiationbeam is indicated with a dashed line throughout the accompanyingfigures. This manufacturing cycle repeats itself, which results inmultiple layers being stacked to form the growing built object 220.Although FIG. 2C shows a single built object 220, it should beappreciated that the large-scale additive manufacturing apparatus 200may be used to additively and simultaneously manufacture multiplesmaller objects in the annular powder bed 202.

Representative examples of suitable materials for a raw material powderused during an additive manufacturing process of the present inventioninclude alloys that have been engineered to have good oxidationresistance, known “superalloys” which have acceptable strength at theelevated temperatures of operation in a gas turbine engine, e.g.Hastelloy, Inconel alloys (e.g., IN 738, IN 792, IN 939), Rene alloys(e.g., Rene N4, Rene N5, Rene 80, Rene 142, Rene 195), Haynes alloys,Mar M, CM 247, CM 247 LC, C263, 718, X-750, ECY 768, 282, X45, PWA 1483and CMSX (e.g. CMSX-4) single crystal alloys. The manufactured objectsof the present invention may be formed with one or more selectedcrystalline microstructures, such as directionally solidified (“DS”) orsingle-crystal (“SX”).

Importantly, in accordance with the present invention, all threeintegral steps of powder deposition, powder leveling and powder meltinghappen concurrently and continuously. Preferably, these three steps ofthe powder-based additive manufacturing process take place concurrentlyand continuously at multiple build areas. For example, at a given pointin time, the powder delivery mechanism 214 deposits the powder 230 at aregion or build area C (not shown) in the powder bed 202; the powderrecoating mechanism 216 levels the powder 230 into a substantially evenpowder layer at a region or build area B (not shown) where the powderdelivery mechanism 214 previously deposited the powder 230; and theirradiation beam directing mechanism 212 melts a selective area (i.e.region or build area A which is not shown) within a substantially evenpowder layer previously leveled by the powder recoating mechanism 216.

The build unit 208 is attached to a rotating mechanism 204 that isoperable to rotate the build unit around the rotational axis 210 360°.In one embodiment, the build unit 208 is directly attached to an area onthe circumference 238 of the rotating mechanism 204. In an alternativeembodiment, a support arm 218 emanates from the circumference of therotating mechanism, upon which at least one of the powder deliverymechanism 214, the irradiation beam directing mechanism 212 and therecoating mechanism 216 is mounted. Alternatively, the build unit 208 isattached to the bottom surface 240, either directly or indirectly via asupport arm.

In FIG. 2B, it is shown that the powder delivery mechanism 214 and theirradiation beam directing mechanism 212 are secured to the support armwhile the powder recoating mechanism 216 is attached to the powderdelivery mechanism 214, specifically at the gate at the bottom portionof the powder delivery mechanism 214 where the powder 230 ‘is dispensed.Since the build unit 208 deposits, levels and melts the powder 230 inthis particular order, it may be advantageous to arrange the relatedthree components imparting these functions such that, in relation to therotational direction indicated by the arrow 236 of the rotatingmechanism 204, the powder delivery mechanism 214 precedes the powderrecoating mechanism 216, which is then followed by the irradiation beamdirecting mechanism 212.

In accordance with the present invention, the rotating mechanism 204 isa rigid structure having a cylindrical configuration as embodied in theaccompanying figures, or alternatively an annular or ring or doughnutconfiguration.

While the build unit 208 is attached to the rotating mechanism 204, therotating mechanism 204 in turn may be attached and supported onto atower 206, for example, via a connector 234. In this embodiment, theconnector is shown as a ball bearing that is sandwiched between an upperrace and a lower race. It would be readily appreciated by one havingskill in the art that any other types of suitable connectors may beused. The tower 206 is a vertically elongated and erect structure, whichas shown in FIG. 2A, oversees the annular powder bed 202. Preferably,also as shown in FIG. 2A, the tower 206, the rotating mechanism 204 andthe annular powder bed are concentric, where the common center is pointX as indicated in FIG. 2C. Preferably, for any given tower and rotatingmechanism, annular powder beds of different sizes can be arrangedconcentrically around them. In other words, the diameter of the powderbed is typically greater than the diameter of the rotating mechanism andthe width or diameter of the tower, although it does not have to be sorestricted.

An irradiation beam directing mechanism used in the present inventionmay be an optical control unit for directing an irradiation beam such asa laser beam. The optical control unit may comprise one or more opticallenses (including telecentric lenses), deflectors, mirrors and/or beamsplitters. Alternatively, the irradiation beam directing mechanism maybe an electronic control unit for directing an electron beam. Theelectronic control unit may comprise one or more deflector coils,focusing coils and/or similar elements. In certain embodiments, theirradiation beam directing mechanism is composed of a diode fiber laserarray (e.g. a diode laser bar or stack) that includes a plurality ofdiode lasers or emitters that each emit a beam of radiation. Acylindrical lens may be positioned between the diode lasers and aplurality of optical fibers. The cylindrical lens compensates for thehigh angular divergence in the direction perpendicular to the diodejunction of the lasers, typically reducing the beam divergence in thefast axis to less than that of the slow axis, thereby easing theassembly tolerances of the overall system compared to an assembly whichdoes not use any coupling optics (i.e., one in which each fiber issimply placed in close proximity to the laser to which it is to becoupled). However, it should be appreciated that diode fiber laserarrays that do not use coupling optics may be used with the presenttechnology. In certain embodiments, the plurality of optical fibers mayfurther include lenses at their respective ends that are configured toprovide collimated or divergent laser beams from the optical fibers. Itshould also be appreciated that even in the absence of these lenses, theends of the optical fibers may be adapted to provide collimated ordivergent laser beams.

In certain embodiments, an irradiation beam directing mechanism inaccordance with the present invention may also include an irradiationsource that, in the case of a laser source, originates the photonscomprising the laser irradiation that is directed by the mechanism. Whenthe irradiation source is a laser source, then the irradiation beamdirecting mechanism may be, e.g. a galvo scanner, and the laser sourcemay be located outside of the build environment. Under thesecircumstances, the laser irradiation may be transported to theirradiation beam directing mechanism by any suitable means, e.g. afiber-optic cable. When the irradiation source is an electron source,then the electron source originates the electrons that comprise theelectron beam or e-beam that is directed by the irradiation beamdirecting mechanism. When the irradiation source is an electron source,then the beam directing mechanism may be, e.g. a deflecting coil. When alarge-scale additive manufacturing apparatus in accordance with thepresent invention is in operation, if the irradiation beam directingmechanism directs a laser beam, then generally it is advantageous toinclude a gas-flow mechanism providing a substantially laminar gas flowin a gas-flow zone. This is because the laser beam used can result insmoke production and the smoke can be condensed when it comes in contactwith the built object, thereby jeopardizing the fidelity of the object.However, if an electron beam is instead used, it is important tomaintain sufficient vacuum in the space through which the electron beamtravels, hence a gas-flow mechanism should not be included in the buildunit.

In further embodiments, an irradiation beam directing mechanism mayinclude one or more electrical slip rings and/or telemetry for improvedcontrol of the movements of the mechanism in the rotating environment ofa powder-based additive manufacturing process of the present invention.

In certain embodiments, the annular powder bed 202 and the central tower206 may be additionally mounted on a stationary support structure 232.In a preferred embodiment, the apparatus 200 is encased within a buildchamber and the atmosphere environment within the chamber, i.e. the“build environment”, or “containment zone”, is typically controlled suchthat the oxygen content is reduced relative to typical ambient air, andsuch that the environment is at a reduced pressure. In some embodiments,the build environment defines an inert atmosphere (e.g., an argonatmosphere). In further embodiments, the build environment defines areducing atmosphere to minimize oxidation. In yet further embodiments,the build environment defines a vacuum.

As the powder-based additive manufacturing progresses and the additivelybuilt object grows, the build platform 228 may be lowered and raisedaccordingly. Accordingly, moving of the build platform upward ordownward, deposition of powder, leveling of powder and beam irradiationoccur simultaneously and continuously. Alternatively, the build platform228 may be vertically stationary but the tower 206 may be configured tobe vertically movable, e.g. move upward and downward as themanufacturing process progresses. Accordingly, moving of the towerupward or downward, deposition of powder, leveling of powder and beamirradiation occur simultaneously and continuously.

In certain embodiments, a build unit having a laser beam irradiationmechanism may advantageously include a gas-flow mechanism with gasinlet(s) and outlet(s) providing a substantially laminar gas flow in agas-flow zone to a build area on the powder bed. This is because thelaser beam used can result in smoke production and the smoke can becondensed when it comes in contact with the built object, therebyjeopardizing the fidelity of the object. However, if an electron beam isinstead used, it is important to maintain sufficient vacuum in the spacethrough which the electron beam travels, hence a gas-flow mechanismshould not be included in the build unit.

The present invention further relates to a large-scale additivemanufacturing apparatus, e.g. the apparatus 300 in FIG. 3 where multiplebuild units 308 may be attached to a central rotating mechanism 304 viasupporting arms 318, which may then be attached and supported onto acentral tower (not shown in this view). The rotating mechanism 304rotates in, for example, the direction indicated by the arrow 336. Eachbuild unit 308 has a powder delivery mechanism 314 (with powder 330), apowder recoating mechanism (not shown in this view) and an irradiationbeam directing mechanism 312. The rotating mechanism 304, the tower andthe annular powder bed 302 are preferably concentric at point X, withthe rotating mechanism 304 and tower being in the center of theapparatus 300 and surrounded by the powder bed 302. Using the powder330, each build unit is operable to additively manufacture a portion ofthe built object 320 in the annular powder bed 302 that is defined by aninner wall 324 and an outer wall 322.

In some embodiments, the build platform of the annular powder bed mayhave a generally subtle helical or spiral configuration that facilitatesinitiation of the continuous additive manufacturing process of thepresent invention (See FIGS. 4A and 4B). For example, when a large-scaleadditive manufacturing apparatus of the present invention has a singlebuild unit, the single helical build platform 428A has a build surface442A that “drops” a single additive growth layer thickness with everyfull 360° revolution of the rotating mechanism. As another example, whena large-scale additive manufacturing apparatus of the present inventionhas multiple build units, e.g. three build units, the triple helicalbuild platform 428B has a build surface 442B that descends a singleadditive growth layer thickness with every 120° or ⅓ revolution of therotating mechanism.

In FIGS. 5A and 5B, a top view and a C-C′ side cross-sectional view of alarge-scale additive manufacturing apparatus 500 are respectively shown.The apparatus 500 includes an annular powder bed 502 with an annularbuild platform 528, inner and outer walls 524, 522. The annular buildplatform 528 having a triple helical build surface 542 (i.e. thestarting point of the three helices indicated with the dashed lines a, band c); a rotating mechanism 504 having a rotational direction asindicated by the arrow 536 and with three build units 508A, 508B, 508Cattached thereto (i.e. to the circumference 538) via supporting arms518A, 518B and 518C; and a tower (not shown) to which the rotatingmechanism is attached and supported onto. Each of the build units 508A,508B, 508C is equipped with their respective beam directing mechanism,powder recoating mechanism powder delivery mechanism.

As shown in FIG. 5B, when multiple build units 508A, 508B and 508C areused, they may be used to deposit the powder 530 and fuse multipleoverlapping additive layers (e.g. “layer A”, “layer B”, “layer C”) in ahelical configuration, similar to a multi-lead screw form. This helicalconfiguration may be more efficient and less problematic than attemptingto use multiple fusing units to form a single additive layer.

A further embodiment of a large-scale additive manufacturing apparatusof the present invention relates to such an apparatus, e.g. theapparatus 600 that, in addition to the powder delivery mechanism 614,powder recoating mechanism 616 and irradiation beam directing mechanism612 in the build unit 608, further includes a central, large andstationary powder supply mechanism 644. Like other apparatuses of thepresent invention described herein, the apparatus 600 includes arotating mechanism 604 configured to rotate around the rotational axis610 in any of the two directions (e.g. direction indicated by the arrow636) and whose circumference the build unit 608 (i.e. the powderdelivery mechanism 614, powder recoating mechanism 616 and irradiationbeam directing mechanism 612) may be attached to, for example, via asupporting arm 618. The rotating mechanism 604 may be supported onto atower 606, for example, via a connector 634 (shown as a ball bearingthat is sandwiched between an upper race and a lower race in thisparticular embodiment).

The powder supply mechanism 644 may be connected to the powder deliverymechanism 614, for example, via a feed chute 646 that preferably rotatesalong with the rotating mechanism 604 in the same direction (e.g.direction indicated by the arrow 636. Preferably, the powder supplymechanism 644, the feed chute 646, the tower 606, the rotating mechanism604 and the annular powder bed 602 are concentric, for example, at pointX as shown in FIG. 6A. Use of the large stationary powder supplymechanism 644 that is connected to the powder delivery mechanism 614 isespecially advantageous because it reduces the weight of the powder 630that is carried by the powder delivery mechanism 614 and also thesupporting arm, both of which rotate during production.

The powder supply mechanism 644 may assume any suitablethree-dimensional configuration. In one particular preferred embodiment,such as the embodiment of FIGS. 6A and 6B, the powder supply mechanism644 is of a conical or funnel shape where the vertex 650 of the cone isconnected to the feed chute 646. In this case, the vertex 650 is smallopening that advantageously allows a controlled flow of the powder 630onto the feed chute 646 and eventually, into the powder deliverymechanism 614.

As described above, a large-scale additive manufacturing apparatus ofthe present invention may be encased within a build chamber. FIG. 6Bshows the build chamber 648 encasing the build unit 608, the tower 606,the rotating mechanism 604 and the annular powder bed 602 and the feedchute 646. The powder supply mechanism 644, on the other hand, ispartially encased at the lower portion of the structure, e.g. the stemof a funnel or the vertex portion of a cone. In alternative embodiments,the feed chute 646 may be partially or not encased within a buildchamber.

The annular powder bed 602 has a build platform 628, a circular innerwall 624 and a circular outer wall 622 with a diameter that is greaterthan the diameter of the inner wall 624. At the beginning of apowder-based additive manufacturing process, the raw material powder isdeposited onto the build surface which is the top surface of the buildplatform 628 (not shown in the FIGS. 6A and 6B views). In someembodiments, such as the embodiment shown in FIGS. 6A and 6B, the innerand outer walls 624, 622 of the annular powder bed 602 each include areceptacle 626 to capture unfused powder spillover during production. Incertain embodiments, the annular powder bed 602 and the central tower606 may be additionally mounted on a stationary support structure 632.

The build unit 608 is operable to perform a powder-based additivemanufacturing process such as but not limited to selective laser melting(SLM), direct metal laser melting (DMLM) and electron beam melting(EBM). During a powder-based additive manufacturing process, the powderdelivery mechanism 614 directionally delivers and deposits a rawmaterial powder 630 onto and/or into the powder bed 602. The powderrecoating mechanism 616 directionally spreads and levels the depositedpowder 630 into a substantially even powder layer, and a portion of thissubstantially even powder layer (i.e. a build area) is then melted bythe laser or electron beam emitted by the irradiation beam directingmechanism 612 to form a fused, additive layer of the built object 620.This manufacturing cycle repeats itself, which results in multiplelayers being stacked to form the growing built object 620. Although FIG.6A shows a single built object 620, it should be appreciated that thelarge-scale additive manufacturing apparatus 600 may be used toadditively and simultaneously manufacture multiple smaller objects inthe annular powder bed 602. As the manufacturing process progresses, thepowder 630 stored in the powder delivery mechanism 614 may bereplenished by the abundant supply in the powder supply mechanism 644via the feed chute 646.

The present invention further provides a method of manufacturing anobject with an apparatus described herein, including an annular object,for example an aircraft component such as but not limited to turbine orvane shroudings, central engine shaft, casings, compressor liners,combustor liners, ducts, etc. In one embodiment, the method includes thesteps of: (a) rotating at least one build unit around a center ofrotation to deposit powder onto a build platform, such that the at leastone build unit moves in a circular path about the center of rotation;(b) irradiating at least one selected portion of the powder to form atleast one fused layer; and (c) repeating at least steps (a) and (b) toform the at least one object. In some embodiments, the method furtherincludes a step (d) of leveling the at least one selected portion of thepowder. Preferably, at least steps (a), (b) and (d) are carried outsimultaneously and continuously. In some embodiments, the method furtherincludes a step of moving the build platform vertically.

In another embodiment, the method of manufacturing includes the stepsof: (a) feeding powder to at least one build unit; (b) rotating at leastone build unit around a center of rotation to deposit the powder onto abuild platform, such that the at least one build unit moves in a paththat is preferably circular about the center of rotation; (c)irradiating at least one selected portion of the powder to form at leastone fused layer; and (d) repeating at least steps (b) and (c) to formthe at least one object. In some embodiments, the method furtherincludes a step of (e) leveling the at least one selected portion of thepowder. Preferably, steps (b), (c) and (e) are carried outsimultaneously and continuously. In some embodiments, the method furtherincludes a step of moving the build platform vertically.

The apparatuses and methods of the present invention may be combinedwith features of the apparatuses and methods described in the followingco-pending patent applications by the applicant:

U.S. patent application Ser. No. 15/406,467, titled “AdditiveManufacturing Using a Mobile Build Volume,” and filed Jan. 13, 2017.

U.S. patent application Ser. No. 15/406,454, titled “AdditiveManufacturing Using a Mobile Scan Area,” and filed Jan. 13, 2017.

U.S. patent application Ser. No. 15/406,444, titled “AdditiveManufacturing Using a Dynamically Grown Build Envelope,”and filed Jan.13, 2017.

U.S. patent application Ser. No. 15/406,461, titled “AdditiveManufacturing Using a Selective Recoater,”and filed Jan. 13, 2017.

U.S. patent application Ser. No. 15/406,471, titled “Large ScaleAdditive Machine,” and filed Jan. 13, 2017.

The disclosures of each of these applications are incorporated herein intheir entireties to the extent they disclose additional aspects ofcore-shell molds and methods of manufacturing that can be used inconjunction with the core-shell molds disclosed herein.

This written description uses examples to disclose the invention,including the preferred embodiments, and also to enable any personskilled in the art to practice the invention, including making and usingany devices or systems and performing any incorporated methods. Thepatentable scope of the invention is defined by the claims, and mayinclude other examples that occur to those skilled in the art. Suchother examples are intended to be within the scope of the claims if theyhave structural elements that do not differ from the literal language ofthe claims, or if they include equivalent structural elements withinsubstantial differences from the literal language of the claims.Aspects from the various embodiments described, as well as other knownequivalents for each such aspect, can be mixed and matched by one ofordinary skill in the art to construct additional embodiments andtechniques in accordance with principles of this application.

The invention claimed is:
 1. An additive manufacturing apparatus,comprising: a plurality of build units, each of the plurality of buildunits comprising a powder delivery mechanism, a powder recoatingmechanism and an irradiation beam directing mechanism; an inner wall andan outer wall; a build platform positioned between the inner wall andthe outer wall, the build platform being movable relative to the innerwall and the outer wall; and a rotating mechanism to which at least aportion of the plurality of build units is attached that providesrotational movement around a center of rotation to the plurality ofbuild units, such that the plurality of build units moves in a circularpath about the center of rotation.
 2. The additive manufacturingapparatus according to claim 1, wherein the build platform is annular.3. The additive manufacturing apparatus according to claim 1, furthercomprising a tower onto which the rotating mechanism is supported. 4.The additive manufacturing apparatus according to claim 1, wherein thebuild platform and the rotating mechanism are concentric.
 5. Theadditive manufacturing apparatus according to claim 3, wherein the buildplatform, the rotating mechanism and the tower are concentric.
 6. Theadditive manufacturing apparatus according to claim 1, wherein at leastportion of the at least one of the plurality of build units is attachedto the circumference of the rotating mechanism.
 7. The additivemanufacturing apparatus according to claim 1, further comprising a buildchamber encasing the apparatus.
 8. The additive manufacturing apparatusaccording to claim 1, further comprising a support arm, wherein at leastportion of the at least one of the plurality of build units is attachedto the rotating mechanism via the support arm.
 9. The additivemanufacturing apparatus according to claim 1, wherein the build platformcomprises an inner wall and an outer wall.
 10. The additivemanufacturing apparatus according to claim 9, further comprising: anouter spill receptacle mounted to the outer wall and being suspendedover a stationary support structure for catching powder spillover; andan inner spill receptacle mounted to the inner wall and being suspendedover the stationary support structure for catching powder spillover. 11.The additive manufacturing apparatus according to claim 1, wherein thebuild platform is non-rotating and vertically stationary.
 12. Theadditive manufacturing apparatus according to claim 1, wherein the buildplatform is non-rotating and vertically movable.
 13. The additivemanufacturing apparatus according to claim 1, wherein the tower isvertically movable.
 14. The additive manufacturing apparatus accordingto claim 1, wherein the irradiation beam directing mechanism comprises alaser source or an electron source.
 15. The additive manufacturingapparatus according to claim 2, wherein the build platform comprises abuild surface that has a helical configuration.
 16. An additivemanufacturing apparatus, comprising: at least one build unit thatcomprises a powder delivery mechanism, a powder recoating mechanism andan irradiation beam directing mechanism; a build platform comprising aninner wall and an outer wall, the build platform being positionedbetween the inner wall and the outer wall and being movable relative tothe inner wall and the outer wall; one or more receptacles to catchpowder spillover positioned adjacent to at least one of the inner wallor the outer wall; and a rotating mechanism to which at least a portionof the at least one build units is attached that provides rotationalmovement around a center of rotation to the at least one build unit,such that the at least one build unit moves in a circular path about thecenter of rotation.